What is the difference between { } and ( ) for command grouping?

{ ...; } groups commands in the current shell (variables persist); ( ... ) runs them in a subshell (a child process, so changes are discarded afterward).

* Brace grouping keeps side effects; subshell parentheses throw them away. *

The practical difference is side effects. Anything you change inside ( ) — variables, the current directory via cd — vanishes when the subshell exits, because it's a separate process. { } runs in your shell, so its changes stick. Both let you apply one redirection to a whole group ({ cmd1; cmd2; } > log).

Use ( ) deliberately when you want isolation — e.g. (cd /tmp && do-stuff) lets you cd temporarily without affecting where you end up. Use { } when you need the results to persist.

Curly braces { } - same shell:

{ echo "one"; echo "two"; } > output.txt
# Both outputs go to file
# Variables persist after

x=1
{ x=2; echo $x; }  # Output: 2
echo $x             # Output: 2 (changed!)

Parentheses ( ) - subshell:

( echo "one"; echo "two" ) > output.txt
# Runs in separate process
# Variables don't persist

x=1
( x=2; echo $x )   # Output: 2
echo $x            # Output: 1 (unchanged!)

Syntax note: Curly braces need:

• Space after {
• Semicolon before }

Go deeper:

• Bash Guide: Compound Commands (Wooledge) — brace grouping (current shell) vs subshell parentheses and their scope effects.